Interfacial Layer Between Fin and Source/Drain Region

ABSTRACT

An embodiment is a semiconductor structure. The semiconductor structure includes a substrate. A fin is on the substrate. The fin includes silicon germanium. An interfacial layer is over the fin. The interfacial layer has a thickness in a range from greater than 0 nm to about 4 nm. A source/drain region is over the interfacial layer. The source/drain region includes silicon germanium.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation application of U.S. patentapplication Ser. No. 17/194,994, filed on Mar. 8, 2021, entitled“Interfacial Layer Between Fin and Source/Drain Region,” which is acontinuation application of U.S. patent application Ser. No. 16/570,144,filed on Sep. 13, 2019, now U.S. Pat. No. 10,944,005, issued Mar. 9,2021, entitled “Interfacial Layer Between Fin and Source/Drain Region,”which is a continuation application of U.S. patent application Ser. No.16/004,677, filed on Jun. 11, 2018, now U.S. Pat. No. 10,483,396 issuedNov. 19, 2019, entitled “Interfacial Layer Between Fin and Source/DrainRegion,” each is incorporated herein by reference in its entirety.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a FinField Effect Transistor (FinFET). FinFET devices typically includesemiconductor fins with high aspect ratios and in which channel andsource/drain regions are formed. A gate is formed over and along thesides of the fin structure (e.g., wrapping) utilizing the advantage ofthe increased surface area of the channel to produce faster, morereliable, and better-controlled semiconductor transistor devices.However, with the decreasing in scale, new challenges are presented.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a flow diagram illustrating a method of manufacturing asemiconductor device, such as a FinFET structure, in accordance withsome embodiments.

FIGS. 2A-2B, 3A-3C, 4A-4B, 5A-5B, 6A-6B, 7A-7B, and 8A-8B illustratevarious views of respective intermediate structures of a semiconductordevice at intermediate stages of manufacturing the semiconductor device,in accordance with some embodiments.

FIGS. 6C-6D are graphs of the atomic percent content of germanium of afin, an interfacial layer, and a source/drain region, in accordance withsome embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments disclosed herein relate generally to forming an interfaciallayer between an epitaxial source/drain region and a fin of a FinFETdevice. For example, the fin may have a recess formed therein, and theinterfacial layer may be formed along surfaces of the recess before theepitaxial source/drain region is formed on the interfacial layer. Incertain embodiments, the interfacial layer may suppress the effects ofsurface impurities formed during the manufacturing stages of a FinFETdevice. In certain embodiments, the interfacial layer may enhanceuniform growth of the epitaxial source/drain region in the recess of afin of a FinFET device.

The fins may be patterned by any suitable method. For example, the finsmay be patterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

The foregoing broadly outlines some aspects of embodiments describedherein. Some embodiments described herein are described in the contextof Fin Field Effect Transistors (FinFETs). Some embodiments aredescribed herein in the context of a replacement gate process.Implementations of some aspects may be used in other processes and/or inother devices. For example, other example processes can include agate-first process, and other example devices include Horizontal GateAll Around (HGAA) FETs, Vertical Gate All Around (VGAA) FETs, nanowirechannel FETs, and other devices. Some variations of the example methodsand structures are described. A person having ordinary skill in the artwill readily understand other modifications that may be made that arecontemplated within the scope of other embodiments. Although methodembodiments may be described in a particular order, various other methodembodiments may be performed in any logical order and may include feweror more steps than what is described herein.

FIG. 1 is a flow diagram illustrating a method 10 of manufacturing asemiconductor device, such as a FinFET structure, in accordance withsome embodiments. The method 10 is described in reference to FIGS. 2A-Bto FIGS. 8A-B. FIGS. 2A-B through 8A-B are cross-sectional views and aperspective view of respective intermediate semiconductor structures 30at intermediate stages in an example process of forming a semiconductordevice in accordance with some embodiments.

FIGS. 2A and 2B illustrate a semiconductor substrate 60, in accordancewith some embodiments. The semiconductor substrate 60 may be or includea bulk semiconductor substrate, a semiconductor-on-insulator (SOI)substrate, or the like, which may be doped (e.g., with a p-type or ann-type dopant) or undoped. In some embodiments, the semiconductormaterial of the semiconductor substrate 60 may include an elementalsemiconductor including silicon (Si) or germanium (Ge); a compoundsemiconductor; an alloy semiconductor; or a combination thereof.

In the embodiments shown in FIGS. 2A and 2B, the semiconductor substrate60 may be a silicon wafer having an area implanted or doped with ann-type dopant to form an n-well 62. Other areas of the semiconductorsubstrate 60 may have other areas implanted or doped with a p-typedopant to form a p-well (not shown). In certain embodiments, a p-typeFinFET device or a p-type metal-oxide semiconductor device (PMOS) isformed over the n-well 62. A concentration of the n-type dopant in then-well 62 can be in a range from about 5×10¹⁶ cm⁻³ to about 1×10¹⁹ cm⁻³.In certain embodiments, an epitaxial layer 64 may be deposited byepitaxial growth over the n-well 62. In certain embodiments, theepitaxial layer 64 is a SiGe (Si_(x)Ge_(1-x)) layer having a germaniumatomic percent content in a range from about 5% to about 40%. In otherembodiments, the epitaxial layer 64 is a SiGe (Si_(x)Ge_(1-x)) layerhaving a germanium atomic percent content in a range from about 40% toabout 80%. The epitaxial layer 64 may also comprise a gradient layerwith a content of an element (e.g., germanium) that varies along thedepth of the epitaxial layer 64. Deposition methods for depositing theepitaxial layer 64 include chemical vapor deposition (CVD), low pressureCVD (LPCVD), atomic layer CVD (ALCVD), ultrahigh vacuum CVD (UHVCVD),remote plasma CVD (RPCVD), vapor-phase epitaxy (VPE), molecular beamepitaxy (MBE), any other suitable deposition processes, or anycombination thereof.

As shown in FIGS. 3A through 3C and at operation 12 of the method 10,fins 74 are formed in the epitaxial layer 64 and the semiconductorsubstrate 60, such as n-well 62. The fins 74 can be formed by etchingtrenches through the epitaxial layer 64 into the semiconductor substrate60, such as into the n-well 62, using appropriate photolithography andetching processes, for example. Isolation regions 78 are formed, each ina corresponding trench. The isolation regions 78 may include or be aninsulating material such as an oxide (such as silicon oxide), a nitride,the like, or a combination thereof. The insulating material may bedeposited by any acceptable deposition process and recessed using anacceptable etch process to form the isolation regions 78. The fins 74protrude from between neighboring isolation regions 78, which may, atleast in part, thereby delineate the fins 74 as active areas on thesemiconductor substrate 60.

In some embodiments, instead of forming the fins 74 from the epitaxiallayer 64, the fins 74 can be formed by etching the trenches into thesemiconductor substrate 60, similar to what was described previously.Hence, the fins 74 can be the same material as the semiconductorsubstrate. In certain embodiments, the semiconductor substrate 60 is asilicon wafer, and the fins 74 are also silicon. Fins 74 are generallydepicted in some of the subsequent figures, which can include or omitthe epitaxial layer 64.

A person having ordinary skill in the art will readily understand thatthe process described above is just an example of how fins 74 may beformed. In other embodiments, a dielectric layer can be formed over atop surface of the semiconductor substrate 60; trenches can be etchedthrough the dielectric layer; epitaxial structures (e.g., homoepitaxialor heteroepitaxial structures) can be epitaxially grown in the trenches;and the dielectric layer can be recessed such that the epitaxialstructures protrude from the dielectric layer to form fins. Fins formedby these processes can have a general structure similar to what is shownin the figures.

As shown in FIGS. 3A through 3C and at operation 14 of the method 10,dummy gate structures 85 are formed over the fins 74. The dummy gatestructures 85 are over and extend laterally perpendicularly to the fins74. Each dummy gate structure 85 comprises a dielectric layer 80, adummy gate layer 82, and a mask 84 . The dielectric layer 80, dummy gatelayer 82, and mask 84 for the dummy gate structures 85 may be formed bysequentially forming respective layers, such as by appropriatedeposition processes, and then patterning those layers into the dummygate structures 85, such as by appropriate photolithography and etchingprocesses. For example, the dielectric layer 80 may include or besilicon oxide, silicon nitride, the like, or multilayers thereof. Thedummy gate layer 82 may include or be silicon (e.g., polysilicon) oranother material. The mask 84 may include or be silicon nitride, siliconoxynitride, silicon carbon nitride, the like, or a combination thereof.

FIG. 3C illustrates the intermediate structure in a three-dimensionalview after the dummy gate structures 85 are formed. Fins 74 are formedon the semiconductor substrate 60, and the fins 74 each protrude aboveand from between neighboring isolation regions 78. In each dummy gatestructure 85, the dielectric layer 80 is along sidewalls and over topsurfaces of the fins 74; the dummy gate layer 82 is over the dielectriclayer 80; and the mask 84 is over the dummy gate layer 82. Source/drainregions 54 a-f are disposed in respective regions of the fins 74 onvarious opposing sides of a respective dummy gate structure 85.

FIG. 3C further illustrates reference cross-sections that are used infigures. Cross-section A-A is in a plane along, e.g., channels in a fin74 between opposing source/drain regions 54 a-c. Cross-section B-B is ina plane perpendicular to cross-section A-A and is across source/drainregion 54 a and source/drain region 54 d in neighboring fins 74. Figuresending with an “A” designation illustrate cross-sectional views atvarious instances of processing corresponding to cross-section A-A, andfigures ending with a “B” designation illustrate cross-sectional viewsat various instances of processing corresponding to cross-section B-B.In some figures, some reference numbers of components or featuresillustrated therein may be omitted to avoid obscuring other componentsor features; this is for ease of depicting the figures.

In some embodiments, after forming the dummy gate structures 85, lightlydoped drain (LDD) regions (not specifically illustrated) may be formedin the fins 74. For example, dopants may be implanted into the fins 74using the dummy gate structures 85 as masks. Example dopants for the LDDregions can include or be, for example, boron for a p-type device andphosphorus or arsenic for an n-type device, although other dopants maybe used. The LDD regions may have a dopant concentration in a range fromabout 10¹⁵ cm⁻³ to about 10¹⁷ cm⁻³.

As shown in FIGS. 4A and 4B, gate spacers 86 are formed along sidewallsof the dummy gate structures 85 (e.g., sidewalls of the dielectric layer80, the dummy gate layer 82, and the mask 84 ) and over the fins 74. Thegate spacers 86 may be formed by conformally depositing one or morelayers for the gate spacers 86, such as by an appropriate depositionprocess, and aniostropically etching, such as by an appropriate etchingprocess, the one or more layers to form the gate spacers 86. The gatespacers 86 may include or be silicon nitride, silicon oxynitride,silicon carbon nitride, the like, multi-layers thereof, or a combinationthereof.

As shown further in FIGS. 4A and 4B and at operation 16 of the method10, recesses 90 are formed in the fins 74. As illustrated, the recesses90 are formed in the fins 74 on opposing sides of the dummy gatestructures 85. The recesses 90 can be formed by an etch process. Theetch process can be isotropic or anisotropic, or, further, may beselective with respect to one or more crystalline planes of thesemiconductor substrate 60 and/or the epitaxial layer 64. Hence, therecesses 90 can have various cross-sectional profiles based on the etchprocess implemented. The etch process may be a dry etch, such as aplasma etch using a processing gas, including but not limited to,tetrafluoromethane (CF₄), chlorine gas (Cl₂), nitrogen trifluoride(NF₃), sulfur hexafluoride (SF₆.

As shown in FIGS. 5A and 5B and at operation 18 of the method 10,interfacial layers 92 are formed over surfaces of the respectiverecesses 90 in the fins 74. The interfacial layer 92 may include or besilicon germanium (Si_(x)Ge_(1-x), where x can be between approximately0 and 1). In certain embodiments, interfacial layer 92 comprises SiGewith a Si atomic percent content of about 90% or more (e.g., in a rangefrom about 90% to about 99.9%) and a Ge atomic percent content of about10% or less (e.g., in a range from about 0.1% to about 10%). In certainembodiments, the interfacial layer 92 is deposited to a thickness 92T ina range from about 1 nm to about 10 nm. In certain embodiment, theinterfacial layer 92 is deposited to a thickness 92T in a range fromabout 1 nm to about 4 nm. In certain embodiments, a first interfaciallayer 92A is formed over a first portion (e.g., in a first recess 90A)of the fin 74; and a second interfacial layer 92B is formed over asecond portion (e.g., in a second recess 90B) of the fin 74. The firstinterfacial layer 92A and the second interfacial layer 92B are formed toa height 92H. The term height 92H of the interfacial layer 92 is definedas the lowest point of the top surface of the interfacial layer 92 inthe recess 90 of the fin 74. In certain embodiments, the variation ofthe height 92H of the first interfacial layer 92A and the height 92H ofthe second interfacial layer 92B is about 5 nm or less, such as in arange from greater than o nm to about 5 nm.

The interfacial layer 92 may be formed in the recesses 90 by epitaxiallygrowing a material in the recesses 90, such as by LPCVD, RPCVD,metal-organic CVD (MOCVD), MBE, liquid phase epitaxy (LPE), VPE,selective epitaxial growth (SEG), the like, or a combination thereof.

One example of a growth process for a SiGe interfacial layer includesperforming an epitaxial growth process at a temperature in a range fromabout 500° C. to about 800° C. The epitaxial growth process may beperformed at a pressure in a range from about 1 Torr to about 100 Torr.Processing gases may include HCl, SiH₄ (silane), SiH₂Cl₂(dichlorosilane), GeH₄ (germane), H₂, or N₂, carrier gas, other siliconprecursors, other germanium precursors, other etching gases, othercarrier gases, and combinations thereof.

In certain embodiments, the interfacial layer 92 may help to suppressthe effects of surface impurities formed over or in the fin 74 duringvarious stages of manufacturing the semiconductor structure 30. Theinterfacial layer 92 can help to cover impurities and can help preventimpurities from entering underlying layers or from diffusing out ofunderlying layers. For example, the impurities may be chlorine, oxygen,carbon, fluorine, and/or silicon species resulting and remaining fromthe etch process at operation 16 in the formation of recesses 90 of thefins 74. For example, the halogen impurities may come from the etchinggases used in a dry etch process, such as CF₄, Cl₂, NF₃, SF₆ etchinggas. The silicon impurities may come from the silicon from the epitaxiallayer 64 comprising SiGe or comprising Si. The oxygen impurities maycome from partial etching of the isolation region 78 comprising siliconoxide. The carbon impurities may come from carbon residual materialsremaining from photoresist or other layers of the semiconductorstructure 30.

Not wishing to be bound by any theory unless specifically set forth inthe claims, the interfacial layer 92 comprising a high amount ofsilicon, such as a Si atomic percent content of about 90% or more (e.g.,in a range from about 90% to about 99.9%), may help to suppress theeffects of surface impurities and reduce roughness. In certain aspects,the high amount of a silicon precursor, such as silane (SiH₄), duringthe formation of the interfacial layer 92 may help to volatilize or toremove the impurities. In certain aspects, the high amount of a siliconprecursor, such as silane (SiH₄), during the formation of theinterfacial layer 92 may help cover or encapsulate the impurities withinthe interfacial layer 92. The interfacial layer 92 may help to act as agetter so that impurities reside in the interfacial layer 92 rather thanin the source/drain region. Impurities in the source/drain region maydisrupt the epitaxial growth and causes non-uniform growth of thesource/drain region. If the thickness of the interfacial layer 92 isless than 1 nm, surface impurities may still remain on the fin 74 or maynot be fully covered by the interfacial layer 92. If the thickness ofthe interfacial layer 92 is greater than 5 nm, the growth of epitaxiallayers thereover to form the source/drain regions may lead toundesirable lattice dislocations in the epitaxial source/drain regionsformed thereover. Lattice dislocations in the epitaxial source regionsmay result in an undesirable lower strain transfer to the channel ofstrain channel devices and may lower device performance.

In certain embodiments, the interfacial layer 92 may help to lower thesurface roughness of the recesses 90 of the fin 74. The surfaceroughness of the recesses 90 of the fin 74 may be over about 2.5 nm RMS.In certain embodiments, the interfacial layer 92 has a surface roughnessof about 2 nm RMS or less, such as in a range from about 0.1 nm RMS toabout 2 nm RMS. In certain embodiments, a smooth interfacial layer 92may help to provide uniform epitaxial growth of an epitaxialsource/drain region thereover. In certain embodiments, a smoothinterfacial layer 92 may help to provide reduced crystal dislocations inan epitaxially grown source/drain region resulting in increasedconductivity of the epitaxial source/drain region and/or increasedadhesion of the epitaxial source/drain region. In certain embodiments, asmooth interfacial layer 92 may help to provide reduced crystaldislocations in an epitaxial source/drain region resulting in increasedstrain characteristics of the channel formed by the fin 74 below thedummy gate structures 85. For example, an epitaxial source/drain region,such as a silicon germanium source/drain region, may induce strain inthe channel to increase the semiconductor device performance. In certainembodiments, a smooth interfacial layer 92 may help to provide uniformlateral and uniform vertical growth of an epitaxial source/drain regionso that the shape of the epitaxial source/drain region may becontrolled. In certain embodiments, a smooth interfacial layer 92 mayhelp to provide uniform growth of an epitaxial source/drain region to auniform size and shape. A uniform size and shape of an epitaxialsource/drain region helps to provide consistent formation of manycontacts to the respective epitaxial source/drain regions.

As shown in FIGS. 6A and 6B and at operation 20 of the method 10, anepitaxial source/drain region 94 is formed over the interfacial layer92. The epitaxial source/drain region 94 may include or be silicongermanium (Si_(x)Ge_(1-x), where x can be in a range from 0 to 1),silicon carbide, silicon phosphorus, silicon carbon phosphorus,germanium, a III-V compound semiconductor, a II-VI compoundsemiconductor, or the like.

In certain embodiments, the epitaxial source/drain region 94 compriseSiGe, the interfacial layer 92 comprises SiGe, and the fin 74 (e.g.,epitaxial layer 64) comprises SiGe. In certain embodiments, theepitaxial source/drain region 94 comprises SiGe with an atomic percentcontent of germanium of about 25% or more (e.g., in a range from about25% to about 70%); the interfacial layer 92 comprises SiGe with anatomic percent content of silicon of about 90% or more (e.g., in a rangefrom about 90% to about 99.9%); and the fin 74 (e.g., epitaxial layer64) comprises SiGe with an atomic percent content of germanium of about5% or more (e.g., in a range from about 5% to about 40%). In certainembodiments, the SiGe source/drain 94 has a germanium atomic percentcontent of about 20% or more greater than the germanium atomic percentcontent of the SiGe fin 74.

In some examples, the epitaxial source/drain regions 94 may also bedoped, such as by in situ doping during epitaxial growth and/or byimplanting dopants into the epitaxial source/drain region 94 afterepitaxial growth. Example dopants for the epitaxial source/drain region94 can include or be, for example, boron for a p-type device andphosphorus or arsenic for an n-type device, although other dopants maybe used. The epitaxial source/drain region 94 (or other source/drainregion) may have a dopant concentration in a range from about 10¹⁹ cm⁻³to about 10²¹ cm⁻³. A source/drain region may be delineated by doping(e.g., by implantation and/or in situ during epitaxial growth, ifappropriate) and/or by epitaxial growth, if appropriate, which mayfurther delineate the active area in which the source/drain region isdelineated.

In certain embodiments, the epitaxial source/drain region 94 maycomprise multiple layers. In certain examples, the epitaxialsource/drain region 94 comprises a first layer (L1), a second layer(L2), and a third layer (L3). In certain embodiments, the epitaxialsource/drain region comprises a first layer of SiGe, a second layer ofSiGe, and a third layer of SiGe, in which each of the layers have adifferent germanium atomic percent content and/or a different dopantconcentration. In certain embodiments, the epitaxial source/drain region94 comprises a first layer of SiGe, a second layer of SiGe, and a thirdlayer of a capping material. The capping material may be or comprise Sior other suitable materials. In certain embodiments, the cappingmaterial can help protect the underlying SiGe from environmentaleffects, such as oxidation and humidity. The capping layer may also beused to form better ohmic contact with a metal used to make electricalcontact with the epitaxial source/drain region 94. In certainembodiments, the capping material can help to protect the underlyingSiGe from outgassing germanium.

Although the epitaxial source/drain region 94 is illustrated as threelayers, the epitaxial source/drain region 94 is not limited to suchlayers. In other embodiments, the epitaxial source/drain region 94 maycomprise one layer, two layers, or more layers. In other embodiments,the epitaxial source/drain region 94 may comprise additional layers(e.g., additional intermediate layer(s), additional outer layer(s)).

As shown in FIG. 6B, two epitaxial source/drain regions 94 are formed asa merged source/drain region. In other embodiments, the epitaxialsource/drain region 94 may be formed as an unmerged doped source/drainregion. The growth of the epitaxial source/drain region 94 may be othershapes depending on the bottom surface of the recess 90 and/or dependingon a lateral and a vertical growth of the epitaxial growth of theepitaxial source/drain region 94 over the interfacial layer 92.

The epitaxial source/drain region 94 may be formed over the interfaciallayer 92 by epitaxially growing a material in the recesses 90, such asby LPCVD, RPCVD, MOCVD, MBE, LPE, VPE, SEG, the like, or a combinationthereof. As illustrated in FIGS. 6A and 6B, due to blocking by theisolation regions 78, the epitaxial source/drain region 94 is firstgrown vertically in the recess 90, during which time the epitaxialsource/drain region 94 may not grow horizontally. After the recess 90 isfully filled, the epitaxial source/drain region 94 may grow bothvertically and horizontally to form facets, which may correspond tocrystalline planes of the semiconductor substrate 60. In some examples,different materials are used for epitaxial source/drain regions forp-type devices and n-type devices. Appropriate masking during therecessing or epitaxial growth may permit different materials to be usedin different devices.

In certain embodiments, the interfacial layers 92A and 92B may be formedto a height 92H with a variation of about 5 nm or less. The height 92Hwith a variation of about 5 nm or less helps epitaxially growth of thesource/drain regions 94A and 94B over the interfacial layer 92 to aheight 94H having a variation in a range from about 0 nm to about 10 nm.For example, the height 94H of a first source/drain region 94A formedover the first interfacial layer 92A and the height 94H of a secondsource/drain region 94B formed over the second interfacial layer 92B aresubstantially uniform. The term height 94H of the source/drain region 94is defined as the highest point of the top surface of the source/drain94.

FIG. 6C is a graph 200 of the atomic percent content of germanium acrossthe fin 74, the interfacial layer 92, the source/drain region 94, andback through the interfacial layer 92, and the fin 74 in a direction 98(as shown in FIG. 6A), in accordance with some embodiments. Thegermanium atomic percent content of the interfacial layer 92 is lowerthan the germanium atomic percent content of the fin 74 and thesource/drain region 94 adjacent to the interfacial layer 92. Thegermanium atomic percent content of the source/drain region 94 is higherthan the fin 74 adjoined by the interfacial layer 92.

FIG. 6D is a graph 300 of the atomic percent content of germaniumthrough the third layer L3, the second layer L2, and the first layer L1of the source/drain region 94, through the interfacial layer 92, andinto fin 74 in a direction 99 (as shown in FIG. 6A), in accordance tosome embodiments. The germanium atomic percent content of theinterfacial layer 92 is lower than the germanium atomic percent contentof the first layer L1 of the source/drain region 94 and the fin 74adjacent to the interfacial layer 92. The germanium atomic percentcontent of the first layer L1 of the source/drain region 94 is higherthan the fin 74 adjoined by the interfacial layer 92. The germaniumatomic percent content of the third layer L₃ of the source/drain region94 is lower than the second layer L2 of the source/drain region 94 buthigher than the first layer L1 of the source/drain region 94.

FIGS. 7A and 7B illustrate the formation of a contact etch stop layer(CESL) 96 and a first interlayer dielectric (ILD) 100 over the CESL 96.Generally, an etch stop layer can provide a mechanism to stop an etchprocess when forming, e.g., contacts or vias. An etch stop layer may beformed of a dielectric material having a different etch selectivity fromadjacent layers or components. The CESL 96 is deposited, such as by anappropriate deposition process, on surfaces of the epitaxialsource/drain regions 94, sidewalls and top surfaces of the gate spacers86, top surfaces of the mask 84, and top surfaces of the isolationregions 78. The CESL 96 may comprise or be silicon nitride, siliconcarbon nitride, silicon carbon oxide, carbon nitride, the like, or acombination thereof. The first ILD 100 may comprise or be silicondioxide, a low-k dielectric material (e.g., a material having adielectric constant lower than silicon dioxide), silicon oxynitride,phosphosilicate glass (PSG), borosilicate glass (BSG),borophosphosilicate glass (BPSG), undoped silicate glass (USG),fluorinated silicate glass (FSG), organosilicate glasses (OSG),SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, silicon carbon material,a compound thereof, a composite thereof, the like, or a combinationthereof. The first ILD 100 may be planarized after being deposited, suchas by a CMP, which may remove the masks 84 from the dummy gatestructures 85 and expose the dummy gate layers 82.

FIGS. 8A and 8B illustrate an intermediate structure after replacing thedummy gate structures 85 with respective replacement gate structures,forming a second ILD 130, and forming contacts 146A, 146B, 146C. Thedummy gate structures 85 are removed, such as by an appropriate etchingprocess, to form trenches. The trenches are filled with respectivereplacement gate structures. The replacement gate structures eachinclude a conformal gate dielectric layer 112, an optional metal linerlayer 114, and a conductive gate fill 116. The conformal gate dielectriclayer 112, optional metal liner layer 114, and conductive gate fill 116can be deposited by appropriate deposition techniques.

The gate dielectric layer 112 is formed conformally in the trench, suchas along sidewall and top surfaces of the fin 74 and along sidewalls ofthe gate spacers 86. The gate dielectric layer 112 may be a siliconoxide, silicon nitride, a high-k dielectric material, or multilayersthereof. A high-k dielectric material, such as a dielectric having a kvalue greater than about 7.0, may include or be a metal oxide or asilicate of Hf, Al, Zr, La, Mg, Ti, Y, Sc, Lu, Gd, Sr, Dy, Ca, Sm, or acombination thereof.

One or a plurality of metal liner layers 114 can be formed conformallyover the gate dielectric layer 112. The metal liner layers 114 caninclude a capping layer, a barrier layer, and/or a work function tuninglayer. A capping layer and a barrier layer can be used to preventimpurities from diffusing into or away from underlying layers. Thecapping layer and/or barrier layer may include tantalum nitride,titanium nitride, the like, or combinations thereof. A work functiontuning layer can be chosen to tune the work function value so that adesired threshold voltage Vt is achieved in the transistor that isformed. Examples of a work function tuning layer include TaAl, TaN,TaAlC, TaC, TaCN, TaSiN, Ti, TiN, TiAlN, Ag, Mn, Zr, Ru, Mo, Al, WN,ZrSi₂, MoSi₂, TaSi₂, NiSi₂, other suitable work function materials, or acombination thereof.

A conductive gate fill 116 is formed over the optional metal liner layer114 (if implemented) and/or the gate dielectric layer 112 and fills thetrench. The conductive gate fill 116 may comprise a metal-containingmaterial such as tungsten (W), cobalt (Co), ruthenium (Ru), aluminum(Al), titanium nitride (TiN), tantalum nitride (TaN), tantalum carbon(TaC), titanium aluminum nitride (AlTiN), titanium aluminum carbon(AlTiC), titanium aluminum oxide (AlTiO), a combination thereof,multi-layers thereof, and other suitable conductive materials.

Portions of the layers for the conductive gate fill 116, the optionalmetal liner layer 114, and the gate dielectric layer 112 above the topsurfaces of the first ILD 100, the CESL 96, and the gate spacers 86 areremoved, such as by a planarization process, like a CMP process.

The second ILD 130 is formed over the first ILD 100, the replacementgate structures, the gate spacers 86, and the CESL 96. Although notillustrated, in some examples, an etch stop layer may be deposited overthe first ILD 100, etc., and the second ILD 130 may be deposited overthe ESL. The second ILD 130 may comprise or be silicon dioxide, a low-kdielectric material, silicon oxynitride, PSG, BSG, BPSG, USG, FSG, OSG,SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, silicon carbon material,a compound thereof, a composite thereof, the like, or a combinationthereof. The second ILD 130 may be deposited by any acceptabledeposition technique.

Openings through the second ILD 130, the first ILD 100, and the CESL 96to the epitaxial source/drain regions 94 are formed to expose at leastportions of the epitaxial source/drain regions 94, such as by usingappropriate photolithography and one or more etch processes. Contacts146 are formed in the openings to the epitaxial source/drain regions 94.The contacts 146 may include a fill metal, such as tungsten, aluminum,cobalt, ruthenium, copper, or other suitable metals. The contacts 146may further include silicide on the respective epitaxial source/drainregions 94 and a barrier and/or adhesion layer between the fill metaland sidewalls of the openings.

It is understood that the semiconductor devices and methods ofmanufacture may also include additional layers, such as photoresistlayers, mask layers, diffusion barrier layers, capping layers, silicideareas, etch stop layers, dielectric layers, adhesion layers, and theother suitable layers. It is understood that the substrate may include aplurality of features (doped regions or wells, fins, source/drainregions, isolation regions, shallow trench isolation (STI) feature, gatestructures, interconnect lines, vias, and other suitable features)formed in, on, and/or over the substrate. The plurality of layers and/orfeatures is used in the fabrication of semiconductor devices andintegrated circuits. The substrate may also include additional materialsformed in, on, and/or over the substrate in the operations of themethods and in the figures as described herein. The semiconductordevices and methods may also include additional manufacturing processesincluding photoresist coating (e.g., spin-on coating), soft baking, maskaligning, exposure, post-exposure baking, developing the photoresist,rinsing, drying, hard baking, inspection, etching, planarization,chemical mechanical polishing (CMP), wet clean, ashing, and/or otherapplicable processes. While the source/drain regions discussed hereinare fabricated using recessed fins, source/drain regions may befabricated by forming source/drain regions over non-recessed fins.

In certain embodiments, a p-type FinFET in a FinFET device is formedover an n-well and/or with p-type/p-doped epitaxial source/drainregions. It is understood that the p-type FinFET devices may also beintegrated with the formation of n-type FinFET devices.

Embodiments disclosed herein relate generally to forming an interfaciallayer, such as an interfacial layer comprising SiGe along surfaces of arecess in a fin between an epitaxial source/drain region and the fin ofa FinFET device. In certain embodiments, the interfacial layer maysuppress the effects of surface impurities formed during themanufacturing stages of a FinFET device. In certain embodiments, theinterfacial layer may enhance uniform growth of the epitaxialsource/drain region in the respective recesses of a fin of a FinFETdevice. In certain embodiments, the epitaxial source/drain regioncomprises p-doped SiGe to induce strain in a channel defined by a gatestructure over the fin.

An embodiment is a semiconductor structure. The semiconductor structureincludes a substrate. A fin is on the substrate. The fin includessilicon germanium. An interfacial layer is over the fin. The interfaciallayer has a thickness in a range from about 1 nm to about 4 nm. Asource/drain region is over the interfacial layer. The source/drainregion includes silicon germanium.

An embodiment is a method of manufacturing a semiconductor device. Themethod includes forming a fin on a substrate. A gate structure is formedover the fin. A recess is formed in the fin proximate the gatestructure. An interfacial layer is formed in the recess. The interfaciallayer includes silicon germanium. A source/drain region is formed overthe interfacial layer by epitaxial growth.

An embodiment is another semiconductor structure. The semiconductorstructure includes a substrate. A fin is on the substrate. A firstinterfacial layer is over a first portion of the fin. A secondinterfacial layer is over a second portion of the fin. The firstinterfacial layer and the second interfacial layer have a heightvariation within 5 nm. A first source/drain region is on the firstinterfacial layer. A second source/drain region is on the secondinterfacial layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a first finand a second fin with an isolation region interposed between the firstfin and the second fin; a first interfacial layer over the first fin anda second interfacial layer over the second fin; and an epitaxialsource/drain region over the first interfacial layer and the secondinterfacial layer, wherein the first interfacial layer and the secondinterfacial layer have an atomic percent content of germanium lower thanthe first fin, the second fin, and the epitaxial source/drain region,wherein the epitaxial source/drain region comprises a plurality ofsilicon germanium layers, wherein each of the silicon germanium layershas an atomic percent content of germanium greater than the atomicpercent content of germanium of the first fin, the atomic percentcontent of germanium of the second fin, and the atomic percent contentof germanium of the first interfacial layer.
 2. The semiconductor deviceof claim 1, wherein the first interfacial layer is separated from thesecond interfacial layer.
 3. The semiconductor device of claim 1,wherein the epitaxial source/drain region comprises SiGe with an atomicpercent content of germanium in a range from about 25% to about 70%. 4.The semiconductor device of claim 1, wherein the epitaxial source/drainregion comprises a first SiGe layer over the first interfacial layer anda second SiGe layer over the first SiGe layer, wherein the first SiGelayer and the second SiGe layer have a different germanium atomicpercent content.
 5. The semiconductor device of claim 4, wherein thesecond SiGe layer contacts an upper surface of the first interfaciallayer.
 6. The semiconductor device of claim 1, wherein the epitaxialsource/drain region comprises one or more SiGe layers and asilicon-containing capping layer over the one or more SiGe layers. 7.The semiconductor device of claim 6, wherein silicon-containing cappinglayer has a lower concentration of germanium then an uppermost layer ofthe one or more SiGe layers.
 8. The semiconductor device of claim 1,wherein the first interfacial layer and the second interfacial layerhave a thickness variation of less than 5 nm along a bottom of the firstinterfacial layer.
 9. A semiconductor device, comprising: a first finand a second fin with an isolation region interposed between the firstfin and the second fin; a gate structure over the first fin and thesecond fin; a first interfacial layer over the first fin adjacent thegate structure and a second interfacial layer over the second finadjacent the gate structure; and an epitaxial source/drain region overthe first interfacial layer and the second interfacial layer, whereinthe first interfacial layer and the second interfacial layer have anatomic percent content of germanium lower than the first fin, the secondfin, and the epitaxial source/drain region, wherein the epitaxialsource/drain region comprises a first SiGe layer over the firstinterfacial layer and the second interfacial layer, a second SiGe layerover the first SiGe layer, and a third SiGe layer over the second SiGelayer, wherein each of the first SiGe layer, the second SiGe layer, andthe third SiGe layer have a different germanium atomic percent content.10. The semiconductor device of claim 9, wherein the first SiGe layerhas a lower germanium atomic percent content than the third SiGe layer.11. The semiconductor device of claim 10, wherein the third SiGe layerhas a lower germanium atomic percent content than the second SiGe layer.12. The semiconductor device of claim 11, wherein the first fin has alower germanium atomic percent content than the first SiGe layer. 13.The semiconductor device of claim 9, wherein the first interfacial layeris separated from the second interfacial layer.
 14. The semiconductordevice of claim 9, wherein the first interfacial layer extends into afirst recess in the first fin, and wherein the second interfacial layerextends into a second recess in the second fin
 15. The semiconductordevice of claim 9, wherein a first height of first interfacial layer iswithin less than about 5 nm of a second height of the second interfaciallayer, wherein the first height is measured at a lowest point of a topsurface of the first interfacial layer and the second height is measuredat a lowest point of a top surface of the second interfacial layer. 16.A semiconductor device, comprising: a first fin with an isolation regionadjacent the first fin; a gate structure over the first fin; a firstinterfacial layer over the first fin adjacent the gate structure; and anepitaxial source/drain region over the first interfacial layer, whereinthe first interfacial layer has an atomic percent content of germaniumlower than an atomic percent content of germanium of the first fin andan atomic percent content of germanium of the epitaxial source/drainregion, wherein the epitaxial source/drain region comprises a first SiGelayer, a second SiGe layer, and a capping layer, wherein the cappinglayer comprises a silicon-containing material.
 17. The semiconductordevice of claim 16, wherein the first interfacial layer has a germaniumatomic percent content in a range between 0.1% and 10%.
 18. Thesemiconductor device of claim 17, wherein a thickness of the firstinterfacial layer is in a range from 1 nm to 5 nm.
 19. The semiconductordevice of claim 17, wherein the first fin under the first interfaciallayer has a surface roughness in a range is greater than 2.5 nm RMS. 20.The semiconductor device of claim 19, wherein the first interfaciallayer has a surface roughness in a range between 0.1 nm RMS and 2 nmRMS.